Patent GB-603172-A (GB)
Title: Improvements in viscosity control instruments
IPC: G01N11/08
Filed: 1945-07-16
Abstract: 603,172. Lubricating. BOOTH, H. T. July 16, 1945, No. 18194. Convention date, Aug. 17, 1944. [Class 12 (iii)] The invention provides an instrument for measuring the change of liquid viscosity arising independently of the viscosity change due to temperature variation and is applicable to the automatic control of a diluent required to be added to the lubricating oil of an aircraft engine. According to the invention the instrument is an independent unit receiving liquid in a path in parallel to the main circulating flow and the changes in viscosity are translated into changes of pressure which actuate a control piston the loading of which piston is varied in response to changes of temperature in the liquid. The viscosity changes are translated into pressure changes by the liquid flowing through a floating friction tube and a plate orifice arranged in series. Dilution ceases when a certain viscosity of lower value is reached, the reduction due to temperature rise being however compensated by an increased loading of the piston. As shown in Fig. 1, the lubricating oil circulated to an aircraft engine 16 is diluted with fuel oil from a branch pipe 25 having a valve 27 held open by a solenoid 28, the circuit to which is opened by a switch 36 incorporated in and under the control of the viscosity measuring instrument 37 when the required dilution has been reached. A hand switch 35 permits the control by the instrument being cut out and the valve 27 being held open by the direct energization of the solenoid 28. A lamp 39 is lit so long as dilution is being effected. The viscosity instrument shown in section in Fig. 4, is supplied with fluid tappedoff from the delivery side of the pump 22 supplying lubricant to the engine. The viscosity is measured by an arrangement of a long tubular viscosity element 89 in combination with a surface orifice 92, whereby a pressure corresponding to the viscosity is set up in a chamber space. The long tubular viscosity element 89 is carried in a piston member 82, sliding in a bushed chamber between ends 45a, 45b, against the action of a spring 87. The fluid enters the instrument through a filter, Fig. 9 (not shown) and passes'by an annular channel 86 and ports 85 controlled by a sleeve 79 of the piston 82 to the left-hand end 45a of the chamber passing thence through the long tubular viscosity element 89 to the end 45b and so to the surface orifice 92 where it passes into a chamber 46b and so to the discharge pipe 52. If the viscosity becomes less then the pressure in the end space 45b will rise and cause the piston to move to the left so that the pressure will rise in the end space 45a, due to the reduced throttling at ports 85. The spring loading of the tube-carrying piston 82 gives a fixed pressure drop between the chambers 45a and 45b and renders the response of the apparatus independent of supply pressure variation. Thus a reduction in viscosity is reflected by a pressure increase at the end 45a (and 45b) and this increase is applied via a groove 64 to cause a spring-loaded piston 65 housed in a chamber between ends 46a, 46b thereof to slide to the right and thereby to allow a bell-crank lever 61 to tilt and so to allow opening of a spring-urged switch housed in a switch casing 53 and held in the closed position when depressed by a plunger 59. The bell-crank lever is tiltably fixed in a diaphragm 63. To prevent operation by viscosity changes arising from mere temperature variation in the fluid the spring loading of this switch release piston 65 is increased with temperature increase by means of an expansible element 69 exposed to the fluid and butting by a stem 72 against an abutment block 74. Thus with a viscosity decrease due solely to a temperature rise the pressure increase at the space 45a which acts on the switch release piston 65 is balanced by an increased loading of the spring 66 and no operation of the switch therefore arises. The instrument is adjustable to give a cut-off at different dilution limits by screw adjustment of the abutment block 74 through a handle 77 provided with index markings and a holding detent, Fig. 3 (not shown). Specifications 576,256 and 576,257 are referred to.